The present invention relates to mounting apparatus for pressure sensitive components, and more particularly to a damped cradle suitable for mounting a piezoelectric surface acoustic wave (SAW) device on a substrate to provide increased vibration control with minimum induced stresses in the SAW device.
SAW devices are pressure sensitive crystals that are used widely in various applications, such as in oscillators and filters. The acoustic/mechanical properties of these devices are critical to their operation, and their physical attachment to a stable support may impact these acoustic/mechanical properties, and thus their operation. Stress related frequency drifts may occur in the SAW devices as a result of their physical attachment to the stable support from two sources. One is caused when large temperature excursions occur and materials having different thermal coefficients of expansion are in contact with the crystal. Another is caused by the physical contact of the support mechanism that produces pressure on the crystal, even when contact is in non-active areas of the crystal. Other mounting means, such as adhesives, may outgas under high vacuum conditions in a hermetically sealed package, contaminating the SAW device surface.
A prior attempt to provide a cradle that reduces the temperature and contact induced stresses on a SAW crystal is disclosed in U.S. Pat. No. 4,845,397 issued July 4, 1989 to Herrick et al entitled "Constraining Mount System for Surface Acoustic Wave Devices." This patent discloses a two-piece cradle that is attached to a substrate, the inner dimensions of which are slightly larger than the outer dimensions of the crystal. Flanges of the cradle overhang the crystal in non-active regions to prevent the crystal from being shaken out of the cradle under vibration, and spacers may be used to prevent appreciable movement within the cradle. However the movement of the crystal within the cradle under vibration is not appreciably damped by this construction.
What is desired is a cradle construction that may be used to mount a SAW device to a stable substrate with minimal induced stress while providing significant damping of motion in a vibration or shock environment.